what does the code snippet Class Abc <R extends XYZ> extends DAO stands for? [closed]

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I have code snippet which is as follows:

public class Abc <R extends XYZ> extends DAO{
.
.
.
}

Can someone explain this snippet? Thanks In advance.

Answer 1

It's a declaration of a class Abc that extends a class DAO (data access object). The generics part <R extends XYZ> says that it can be used to insert, update and/or delete objects R that extend the class XYZ (most probably a data transfer object). Now, there's no declaration of the R class. It's just a placeholder to whatever class extending XYZ.

Answer 2

Abc is a subclass of DAO and also includes a generic R which is a subclass of type XYZ

Answer 3

Your class Abc is a subclass of class type DAO. This means that the following will compile:

DAO abc = new Abc();

Secondly, your Abc class has defined a generic type, R. This type must be a subclass of XYZ. This means that for any class that can be referred to as XYZ, can be used to add genericity to this class Abc.

public class ARGH extends XYZ { }

Abc<ARGH> abc = new Abc<ARGH>();

This means that for any type R inside Abc, it will now be of type ARGH.

public class Abc <R extends XYZ> extends DAO {
    R element;

    public Abc(R element) {
       this.element = element;
    }
}